Appellants, the tenants and guests residing in a two-family building in a high crime area of the city, sued the landlord for injuries resulting from a fire deliberately set in the foyer of the building by the former paramour of one tenant. Appellants alleged that the landlord was negligent in blocking alternate exits and failing to provide a lock on the outer door of the foyer, despite his knowledge of previous criminal acts occurring in the common area of the building under his exclusive control. The trial judge granted the landlord-appellee’s motion for summary judgment, stating that, as a matter of law, (1) the landlord had no duty to foresee that a tenant’s rejected lover would commit criminal arson and (2) any violations of housing regulations were not the proximate cause of the injury. We reverse the grant of summary judgment because the existence of the landlord’s duty and causation are questions of fact for the jury.
In August, 1975, the two story building at 507 0 Street, N.W., was cited by the Department of Economic Development for numerous.continuing violations of the housing regulations, including an outer door which did not fit reasonably well within its frame and defective or missing hardware on the door. In the same month, Gloria Graham and family moved into the downstairs apartment and Priscilla Harris and family moved into the upstairs apartment.
Although there was no lock on the outer door, each apartment did have a lock on the inner door leading directly into the individual premises. The tenants frequently complained to the landlord about the absence of an outer door lock. They explained to the rental agent that intruders and strangers entered the foyer through the open door and committed acts of vandalism, such as removing the lights or fuses. Both tenants were aware of the neighborhood's reputa*105tion as a high crime area, and Ms. Graham told the rental agent of an attempted burglary through her window.
A week before the fire, Ms. Graham told the rental agent that she had lost the key to her back door, and asked for a replacement, but none was provided. Ms. Harris had no rear exit because a rear stairway leading to her back door had been boarded up before her tenancy began.
The day before the fire, on Friday, June 5, 1976, Ms. Harris quarrelled with Tony Totten, her boyfriend of six years, and evicted him from her apartment, where he had been living. The police were called to supervise the eviction of Totten and his possessions. In deposition, Ms. Harris stated that the only people who had keys to her apartment were her son, niece and herself; she did not state that Totten had a key, but mentioned that he had entered her apartment on a former occasion by manipulating the lock with a screwdriver or case knife.
On the night of Saturday, June 6, Totten returned to 507 0 Street and poured and ignited an inflammatory liquid in the foyer. One boy was killed in the ensuing fire, several other people received serious burns, and others were injured by jumping from the windows. Totten subsequently pleaded guilty to second-degree murder.
Those injured in the fire brought a personal injury action against the landlord. They charged him with negligence in failing to provide an outer door lock and a replacement key for Ms. Graham’s back door, and in boarding up the rear stairway. The trial court granted summary judgment in favor of the landlord, stating in a Memorandum and Order that the landlord had no duty to foresee that a regular guest of a tenant might commit arson unless front door locks were provided. Moreover, concluded the court, the blocked staircase or missing back door key could not be said to be the proximate cause of the injuries. In granting the summary judgment motion, the trial judge also commented that the absence of an outer door lock was not the proximate cause of the injuries, because a former guest would have been able to gain access no matter how many locks were in place.
It is established in the District of Columbia that a landlord has a duty to use reasonable care to keep safe those common areas of the building retained under his control. Walker v. Dante, 61 U.S.App.D.C. 175, 58 F.2d 1076 (1932). See also, Levine v. Katz, 132 U.S.App.D.C. 173, 174, 407 F.2d 303, 304 (1968) (physical defect leading to plaintiff’s injury). This duty has been extended to encompass situations where third party criminal acts injure tenants on the premises, when the criminal activity should have been foreseen by the landlord. E. g., Ramsay v. Morrissette, D.C.App., 252 A.2d 509 (1969) (issue for jury whether decreased security measures make landlord liable for assault in apartment); Kline v. 1500 Massachusetts Avenue Apartment Corp., 141 U.S. App.D.C. 370, 439 F.2d 477 (1970) (assault in hallway of large building where security measures in effect at beginning of lease had been discontinued; liability based on lease as contract). On facts similar to these, in Spar v. Obwoya, D.C.App., 369 A.2d 173 (1977), we held that evidence was sufficient to uphold a negligence verdict against a landlord when a tenant was assaulted in his apartment hallway after an outer door lock had been broken for a week and tenants had complained about the front door security-
Foreseeability is the key element in establishing the landlord’s duty. Whether the landlord could foresee the criminal activity which caused the injuries here is a question of fact. The Kline court defined “foreseeable” as “probable and predictable” 141 U.S.App.D.C. at 376, 439 F.2d at 483 (emphasis in original). Appellees contend that the minor acts of trespass and vandalism in the foyer of which appellants complained to the rental agent are so different in scope from arson which caused the injuries that the prior events did not constitute notice. We think that a jury might conclude otherwise. Both parties admit that the neighborhood was high in criminal activity. It was alleged that the outer door did not close properly, facilitating entry to *106nontenants. Ms. Graham alleged she had informed the rental agent about a previous attempt at robbery through her window. These circumstances create a triable issue of fact as to whether the danger of a criminal assault by means of arson was sufficiently probable and predictable to create a duty in the landlord to take reasonable precautionary measures. In Spar v. Obwoya, supra at 177, the landlord was said to be put on notice by previous burglaries and the presence of unauthorized persons in the building.
Appellees also argue that the landlord’s duty extends only to keep out unknown intruders, not guests of tenants. Similarly, the trial court stressed the fact that the arsonist had been allowed to live on the premises until the day before the fire, so that it was unreasonable to impose a duty on the landlord to keep him from injuring the tenants. If the arsonist had been another tenant, or had he been unquestionably a guest who possessed a key, then perhaps, as a matter of law, no duty could be imposed on the landlord to keep him from assaulting the tenants. See Trice v. Chicago Housing Authority, 14 Ill.App.3d 97, 100, 302 N.E.2d 207, 209 (1973) (no duty to insure tenants’ safety from another tenant’s act of throwing TV over stair railing). Here, however, facts have been alleged which make the criminal’s rightful access to the building an issue of fact for the jury. Ms. Harris stated in her deposition that Totten was ejected from the building under police supervision and that he had never had a key. The jury could conclude that he was no longer a guest, and that the tenants had as much legitimate expectation to keep him off the premises as they would any other intruder.
For negligence to exist, the landlord not only must have foreseen the danger, but also he must have failed to take security measures reasonable under the circumstances. Spar v. Obwoya, supra at 177; Kline v. 1500 Massachusetts Avenue Apartment Corp., supra 141 U.S.App.D.C. at 378-79, 439 F.2d at 485-86. No District of Columbia court has ever imposed on landlords “a general legal duty ... to provide full time resident managers or to install locks on the front door of an apartment house.” Ramsay v. Morrissette, supra at 512-13. What measures are reasonable under the circumstances is determined by a jury assessment of protective measures taken in buildings of similar character and class. Spar v. Obwoya, supra at 177-78; Kline v. 1500 Massachusetts Avenue Apartment Corp., supra 141 U.S.App.D.C. at 379, 439 F.2d at 486.
Each of the three cases in the District of Columbia discussing the landlord’s duty involved a crime in an apartment building. The Kline court specifically singled out the landlord of an “urban multiple unit apartment dwelling” id. at 376, 439 F.2d at 483, as owing the duty of protection. The building here was not a “multiple unit apartment,” so the duty owed may be less. For one thing, the tenants of a duplex might be able to exercise more control over their own safety. The controlling reason for imposing a tort duty in Kline was that the apartment tenant would find it impossible to provide the security in common areas. See Note, Landlord's Duty to Protect Tenants from Criminal Acts of Third Parties: The View from 1500 Massachusetts Avenue, 59 Geo. L.J. 1153, 1187 (1971) (degree of protection expected of landlord should increase with size of building because tenants’ control over common areas decreases). It could also be found that the apartment dweller is in greater need of protection. See Comment, Landlord-Tenant Law: Landlord Held Negligent for Criminal Assault by Third Party Intruder on Tenant, 55 Minn.L. Rev. 1097, 1109 & n.72 (1971) (most New York City robberies occur in common areas of apartment houses). The jury must consider what type of security measures are commonly employed in duplexes in similar areas of the city where low rents are charged.
Whether the landlord has a duty to provide rear exits must also be determined according to what is reasonable under all the circumstances. The District of Columbia Housing Code and Housing Regulations *107do not require a second stairway in a two story, two unit building. D.C. Building Code 1972, 5A-1 DCRR § 616.2.
If negligence is found, it must then be decided if the injuries were proximately caused by the landlord’s failure to provide a front door lock or rear exits. The issue of proximate causation is one of fact. Ramsay v. Morrissette, supra at 512 (both duty and causation are issues for jury); Kline v. 1500 Massachusetts Avenue Apartment Corp., supra 141 U.S.App.D.C. at 382, 439 F.2d at 489 (MacKinnon, J., dissenting) (case should have been remanded for determination whether absence of lock was, in fact, the cause of the assault, or whether assailant was a tenant or guest rather than intruder).1 Of course, it is possible that the arsonist would have found a way to burn the premises and assault his victims without entering the foyer. This possibility, however, cannot be presumed as a matter of law. As we said in Spar v. Obwoya, supra at 178, the jury does not need to find “that an adequately secured door would have in all events deterred the assailant.” The jury might find that Totten would have had a key to the outer door lock even if such a lock had been in place. But this determination is best made by the jury which can assess, for example, the credibility of Ms. Harris’ denial that Totten had any key to the inner door.
Totten’s intervening criminal act will not necessarily excuse the landlord from liability. In Spar v. Obwoya, supra, we accepted the Restatement of Torts § 448 test for causation where a landlord’s failure to provide a lock arguably permitted an intruder to enter the premises and assault tenant:
The act of a third person in committing an intentional tort or crime is a superseding cause of harm to another resulting therefrom, although the actor’s negligent conduct created a situation which afforded an opportunity to the third person to commit such a tort or crime, unless the actor at the time of his negligent conduct realized or should have realized the likelihood that such a situation might be created, and that a third person might avail himself of the opportunity to commit such a tort or crime. [Restatement (Second) of Torts § 448 (1965) (emphasis supplied).]
See also, Johnston v. Harris, 387 Mich. 569, 572, 198 N.W.2d 409, 410 (1972) (when a tenant was assaulted by assailants hiding in his unlocked vestibule, proximate causation can be found under Restatement of Torts § 448 because “in a high crime district it is reasonably foreseeable that inadequate lighting and unlocked doors would create conditions to which criminals would be attracted. . . .”).
The foreseeability of the criminal activity is a decisive factor in determining causation, as it is in determining duty. Prosser says that the issue of causation is subsumed in the issue of duty. Where criminal acts operate on a background created by defendant, the real issue is whether the defendant should be responsible for the intervening criminal acts. “It is only where such misconduct was to be anticipated, and the risk of it was unreasonable, that liability will be imposed for such intervening acts.” W. Prosser, Law of Torts § 44, at 283 (4th ed. 1971).
Thus, the question of proximate causation depends on whether the crime was foreseeable. As we have said already in our discussion of duty, that determination is one for the trier of fact. Where reasonable men might differ over the question of whether an intervening force is a reasonable, foreseeable consequence of defendant’s conduct, the issue of probable cause should not be determined as a matter of law. See, e. g., Wright v. General Motors Corp., 479 F.2d 52, 53 (7th Cir. 1973) *108(question for jury whether defects in truck which caused it to stop were proximate cause of truck driver’s injury, or whether wrongful conduct of oncoming vehicle which struck truck driver was intervening force which could relieve manufacturer of liability). Spain v. McNeal, D.C.App., 337 A.2d 507 (1975); Wagshal v. District of Columbia, D.C.App., 216 A.2d 172, 175 (1966) (issue of fact whether District should have foreseen injury to one motorist from another when stop sign was not maintained).
In conclusion, we hold that the trial court erred in granting appellees’ motion for summary judgment. The landlord could have been negligent in failing to foresee that a crime in the foyer would injure appellants, and in failing to take reasonable security precautions like those taken in housing of similar character and class. It is a question of fact for the jury whether negligence existed and whether such negligence proximately caused the tenants’ injuries. Consequently, we reverse so that these issues may be resolved at trial.
So ordered.
. The Kline case was reversed in favor of the tenant and remanded for a determination of damages only. The majority held that the landlord owed a duty of protection under tort law and contract law. Viewing the lease as a contract, the duty was measured by the security precautions in effect at the beginning of the lease. [Judge MacKinnon, dissenting, argued that insufficient facts were proved at trial to say that landlord had breached any duty owed.]