Plaintiffs-appellants are six family members, one of whom, Celso Rodriguez-Cirilo (“Celso”), was the victim of a stabbing. Cel-so was stabbed by his brother, Francisco Rodriguez-Cirilo (“Francisco”), who is not a party to the suit. The family members filed a civil rights damages action under 42 U.S.C. § 1983 (1994) against two officers of the *51Puerto Rico Police Department alleging that the officers’ failure to enforce a temporary detention order against Francisco caused the injury to Celso and thus violated his constitutional rights.1
The district court held that plaintiffs failed to establish that a due process right protected under section 1983 was violated by the officers’ failure to prevent private violence, and also held that plaintiffs could not establish causation. Having reviewed the record and the parties’ briefs on appeal, we find that the district court’s treatment of the causation issue correctly identifies a sufficient ground for granting summary judgment to the defendants. We therefore do not reach the nettlesome legal question of whether, in light of DeShaney v. Winnebago County Dept. of Social Servs., 489 U.S. 189, 109 S.Ct. 998, 103 L.Ed.2d 249 (1989), a police officer’s knowing refusal to carry out the express terms of a non-diseretionary detention order can be deemed an “affirmative act” that, by increasing the risk of private harm to those sought to be protected by the order, may trigger due process concerns. Cf. DeShaney, 489 U.S. at 201, 109 S.Ct. at 1006; Frances-Colón v. Ramírez, 107 F.3d 62, 64 (1st Cir.1997) (discussing the limited scope for relief under section 1983 where “the government employee, in the rare and exceptional case, affirmatively acts to increase the threat of harm to the claimant”); Soto v. Flores, 103 F.3d 1056, 1064 (1st Cir.1997) (“In a creation of risk situation, where the ultimate harm is caused by a third party, courts must be careful to distinguish between conventional torts and constitutional violations.”).
BACKGROUND
In the summary judgment context, we relate all material facts in genuine dispute in the fight most favorable to the party resisting summary judgment, here the plaintiffs. Sánchez v. Alvarado, 101 F.3d 223, 225 n. 1 (1st Cir.1996). On March 16, 1994, Jorge Rodríguez-Nieves (“Jorge”), a nephew of both Celso and Francisco who is not a party in the instant suit, filed a petition pursuant to the Mental Health Code of Puerto Rico (“Law 116”),2 to have his uncle Francisco involuntarily detained for psychiatric examination. The petition stated that Francisco presented a danger to himself and others and had threatened to kill with a sharp object, such as a machete or a knife. On March 17, 1994, a San Juan municipal court judge responded to the petition by issuing an order that Francisco be detained for examination. The temporary detention order authorizes a law enforcement officer to detain the subject — with the assistance of health care personnel if necessary — and to take him to a psychiatric institution where he can be examined, and where he cannot be held for more than 24 hours. If the examining doctor concludes that detention for any longer period or treatment of the subject is required, then that doctor must notify the petitioner, who must then notify the court. The temporary detention order under Law 116 does not explicitly give police officers any discretion with regard to enforcement.3
On the same day that the order was issued, Jorge, along with two of Francisco’s siblings (but not Celso), went to a police station to have the order enforced. The defendants were at the police station and assumed the task of enforcing the order, calling on paramedics for assistance. Later that day, the defendant police officers, the paramedics, and the three family members found Francisco at a local establishment. Francisco refused to go with the officers, stating that he was already being treated at a veteran’s hospital. The officers then failed to carry out the order, despite the efforts of the family members to convince the officers that Francisco was dangerous. Before departing, the officers told the family members that they themselves should take Francisco to a veteran’s hospital for treatment, which is *52contrary to the stated procedure under Law 116.
No further legal steps were taken to obtain another detention order, although the plaintiffs and other family members assert that they made further informal requests to the police to take Francisco into custody. Francisco was ultimately never taken to a hospital for examination or treatment. On April 6, 1994, nearly three weeks after the defendants’ failure to carry out the temporary detention order, the injury giving rise to this damages suit occurred. Francisco stabbed his brother Celso while Celso was at their mother’s house for a visit. Celso had argued with Francisco about getting their mother some water and then stood out on a balcony; a few minutes later Francisco returned and stabbed Celso in the chest with a knife. Celso suffered injuries to his chest and to his respiratory and digestive systems.
Plaintiffs brought actions for damages under both section 1988 and Puerto Rico tort provisions. The district court granted summary judgment to defendants on the section 1983 suit and dismissed the state tort claims without prejudice.
DISCUSSION
We review the district court’s grant of summary judgment de novo. Serrano-Cruz v. DFI Puerto Rico, Inc., 109 F.3d 23, 24 (1st Cir.1997).
The essential elements of a claim under section 1983 are: First, that the defendants acted under color of state law; and second, that the defendants’ conduct worked a denial of rights secured by the Constitution or by federal law. Martínez v. Colón, 54 F.3d 980, 984 (1st Cir.1995). To satisfy the second element, plaintiffs must show that the defendants’ conduct was the cause in fact of the alleged deprivation. See Gutiérrez-Rodríguez v. Cartagena, 882 F.2d 553, 559 (1st Cir.1989). The issue of causation of damages in a section 1983 suit is based on basic notions of tort causation. See Maldonado Santiago v. Velázquez García, 821 F.2d 822, 831 (1st Cir.1987) (“Section 1983 imposes a causation requirement similar to that of ordinary tort law.”). In applying basic tort principles to the facts raised by a particular section 1983 claim, the causation requirement may be fleshed out with reference to state law tort principles. Gutiérrez-Rodríguez, 882 F.2d at 561.
As discussed in the decision below, plaintiffs cannot establish that the conduct of the defendants, in not enforcing the temporary detention order, was the legal cause of an attack occurring much later. See Rodríguez-Cirilo v. García, 908 F.Supp. 85, 91 (D.P.R.1995). The concept of proximate causation restricts tort liability to those whose conduct, beyond falling within the infinite causal web leading to an injury, was a legally significant cause. The passage of time can certainly reduce the legal significance of a particular contributing act. See Restatement (Second) of Torts § 433 (1965) (lapse of time a factor to be considered in determining whether a contributing factor is substantial).
The remoteness in time of the harm in this case precludes a finding of proximate causation. Although Francisco committed the kind of violence mentioned in the petition for a detention order, the space of over two weeks that passed after the officers’ failure to detain Francisco, during which time family members did not attempt to obtain another detention order, renders his later act of violence too remote to impose liability on the officers. Cf. Martínez v. California, 444 U.S. 277, 285, 100 S.Ct. 553, 559, 62 L.Ed.2d 481 (1980) (murder committed by parolee five months after release “too remote” a consequence to hold parole board liable under section 1983); Restatement (Second) of Torts § 433 (1965). Although the stabbing occurred at the address named in the original petition, and although the police officers may have had-some indication that Celso would be at danger from an attack by Francisco,4 giv*53en the intervening time we cannot say that the officers’ failure to enforce the order was the legal cause of the injury. See Martínez, 444 U.S. at 285, 100 S.Ct. at 558-59; Restatement (Second) of Torts § 433 cmt. f (“Experience has shown that when a great length of time has elapsed between the actor’s negligence and harm to another, a great number of contributing factors may have operated, many of which may be difficult or impossible of actual proof_ [T]he effect of the actor’s conduct may thus be so attenuated as to be insignificant-”).
What further persuades us that the causation issue in this case is dispositive is that even if Francisco had been taken to a hospital on March 17, 1994, for examination, appellants have not shown that an examination performed on that day would have prevented the violent attack, spurred by an argument, on April 6, 1996. The temporary detention period was itself limited to a maximum of twenty-four hours. Appellants offered no competent evidence that could have supported a finding that an examination in Francisco’s particular ease would have prevented the later attack. Appellants rely on a clinical psychologist’s signed statement asserting that Francisco’s “personality disorder” caused the stabbing, and that, had Francisco been detained on March 17, 1994, he would have received effective treatment that would have prevented the stabbing. This statement, based solely on information collected through conversations with Francisco’s relations and formed without any direct examination of either Francisco or of his medical records, is not enough to defeat defendants’ motion for summary judgment and does not create a triable issue of material fact as to causation.5 “The nonmoving party must establish a trial-worthy issue by presenting ‘enough competent evidence to enable a finding favorable to the nonmoving party.’ ” Le-Blanc v. Great Am. Ins. Co., 6 F.3d 836, 842 (1st Cir.1993) (quoting Anderson v. Liberty Lobby, Inc., 477 U.S. 242, 249, 106 S.Ct. 2505, 2510-11, 91 L.Ed.2d 202 (1986)). Thus, not only do appellants run into proximate causation problems, but their case also falls short with regard to demonstrating the “but for” aspect of causation. See Restatement (Second) of Torts, § 432 (1965). We conclude, therefore, that defendants were properly granted summary judgment based on plaintiffs’ failure to demonstrate causation under well-established tort principles.
Appellants’ remaining arguments on appeal do not require lengthy treatment. First, we note that the record indicates that the appellants have failed to support, with any competent evidence, their additional assertion that there existed a conspiracy between the defendants and Francisco to violate plaintiffs’ civil rights. Second, in response to appellants’ claim that the district court abused its discretion in denying them an opportunity to amend their complaint after the deadline for such amendments established in the court’s scheduling order, we note that even had the plaintiffs been able to amend their complaint by adding as a third defendant the supervisor of the two defendant police officers, the fundamental, insurmountable obstacle of causation would still have remained, and would still have offered a sufficient ground for summary judgment in favor of defendants.
CONCLUSION
For the foregoing reasons the district court’s grant of summary judgment to defendants is affirmed.
.In view of the ambiguous wording of the plaintiffs’ complaint, the district court chose to treat this section 1983 suit as one claiming a violation of due process under the Fourteenth Amendment. On appeal, neither party suggests otherwise.
. See P.R. Laws Ann. tit. 24 § 6006 (Supp. 1991).
. Defendants appear to concede the fact that carrying out the terms of such a Law 116 order is a non-discretionary obligation on the part of the police officer.
. It is a widely recognized tort law principle that one may be responsible for the foreseeable intervening acts of third parties. For example, the requirement of "causalidad adecuada” under Puerto Rico tort law would permit the assignment of liability if the intervening third party action' — that is, Francisco's stabbing — was a reasonably foreseeable consequence of the defendants' actions. Widow of Andino v. Puerto Rico Water Resources Auth., 93 P.R.R. 168, 177-79 *53(P.R.1966) (harm caused by reasonably foreseeable intervening causes, including the actions of third parties, may lead to liability).
. This statement, as the district court notes, would probably be found unreliable and inadmissible as expert testimony under Fed.R.Evid. 702. Garcia, 908 F.Supp. at 91-92. In any event, the psychologist's broad assertion regarding causation does not create a triable issue in this case, where the defendant's case as to a lack of proximate causation is strong.