delivered the opinion of the court:
On November 2, 1984, plaintiff, Richard Wakeford, and his wife, Dawn, had dinner at the Ramada Inn restaurant in Alton, Illinois. At approximately midnight, the couple left the restaurant and approached their car, which was parked near the restaurant’s exit. At this time, an unidentified man with a gun approached plaintiff as he unlocked the passenger side door. The man shot three times, striking plaintiff in the temple, ear, chest and left hand. The assailant then fled and has never been identified.
Plaintiff filed suit in the circuit court of Madison County against defendant, Rodehouse Restaurants of Missouri, Inc., the owner of the Ramada Inn. The complaint alleged that by failing to provide security guards and adequate lighting in the parking lot, defendant failed to reasonably protect its patrons. The complaint alleged that this failure constituted negligence as well as willful and wanton misconduct.
During his opening statement at trial, defense counsel stated that he would be calling two Alton police officers to testify about the need for security guards at the Ramada Inn. Plaintiff objected on the grounds that no police officers had been disclosed as expert witnesses under Supreme Court Rule 220 (134 Ill. 2d R. 220). The court overruled this objection.
During the trial, defendant took the evidence deposition of Alton police officer Robert Lahlien as a witness. Officer Lahlien was one of the officers who investigated the shooting. He testified that he had lived in Alton all his life and been a police officer there since August of 1972. As part of his duties with the Alton police department, Lahlien is required to review crime reports on a daily basis. Lahlien also reviewed the police department’s index card file wherein crimes are categorized by geographical area. Over plaintiff’s objections, Lahlien testified that, in his opinion, the Ramada Inn was not located in a high-crime area and that he did not believe a security guard was necessary at the hotel.
The jury returned a verdict in favor of defendant. On appeal, the appellate court reversed and remanded for a new trial. (223 Ill. App. 3d 31.) The appellate court held that it was error to permit Officer Lahlien’s testimony because he should have been disclosed as an expert witness under Rule 220. (223 Ill. App. 3d at 42.) The appellate court also held it was error for defendant to cross-examine plaintiff regarding the insurance benefits he received under his wife’s policy. We granted defendant’s petition for leave to appeal. 134 Ill. 2d R. 315.
Supreme Court Rule 220(aXl) defines an expert witness as someone “who, because of education, training or experience, possesses knowledge of a specialized nature beyond that of the average person on a factual matter material to a claim or defense in pending litigation and who may be expected to render an opinion within his expertise at trial.” (134 Ill. 2d R. 220(a)(l).) Defendant concedes that based on Lahlien’s experience and training as a police officer he was an expert witness under Supreme Court Rule 220(a).
At issue in this case is whether Lahlien was subject to the disclosure and discovery requirements of Rules 220(b) and (c). Rule 220(b)(l) provides in part:
“In order to insure fair and equitable preparation for trial by all parties the identity of an expert who is retained to render an opinion at trial on behalf of a party must be disclosed by that party [no later than 60 days before trial] ***. Upon disclosure, the expert’s opinion may be the subject of discovery as provided in paragraph (c) hereof. Failure to make the disclosure required by this rule or to comply with the discovery contemplated herein ■will result in disqualification of the expert as a witness.” (Emphasis added.) (134 Ill. 2d R. 220(b)(1).)
Rule 220(c) provides that upon being served with interrogatories a party “retaining or employing” an expert witness must disclose the subject matter of the expert’s expected testimony, the expert’s opinion on the matter, the bases for that opinion and the expert’s qualifications. (134 Ill. 2d R. 220(c)(1).) Rule 220(c) also requires a party to “seasonably supplement” the answers to interrogatories under that rule. 134 Ill. 2d R. 220(c)(3).
Defendant contends that Lahlien is not subject to the disclosure requirements of Rule 220(bXl) because he was not “retained” as an expert. Defendant relies on this court’s opinion in Tzystuck v. Chicago Transit Authority (1988), 124 Ill. 2d 226, as support for this assertion. In Tzystuck this court held that even though a treating physician is an expert witness under Rule 220(a), his identity as an expert need not be disclosed prior to trial. This court reasoned:
“[Rule 220(bXl) requires] litigants to disclose the identity and opinions only of those witnesses who are engaged for the purpose of giving an expert opinion at trial. It may be said that the connection between a medical expert who is ‘retained to render an opinion at trial’ and the party to the suit may be litigation-related, rather than treatment-related. Treating physicians, on the other hand, typically are not ‘retained to render an opinion at trial’ but are consulted, whether or not litigation is pending or contemplated, to treat a patient’s physical or mental problem. While treating physicians may give opinions at trial, those opinions are developed in the course of treating the patient and are completely apart from any litigation. Such an opinion is not formed in anticipation of trial, but is simply the product of a physician’s observations while treating the patient, which coincidentally may have value as evidence at trial. In this respect, the opinions of treating physicians are similar to those of occurrence witnesses ***.” Tzystuck, 124 Ill. 2d at 234.
In Tzystuck, this court noted that Rule 220 was designed to “facilitate trial preparation and the evaluation of claims by eliminating the late or surprise disclosure of experts at trial.” (Tzystuck, 124 Ill. 2d at 238.) In this light, it was significant that the identity of the examining physician was disclosed and that the doctor could have been deposed under Supreme Court Rule 204. (Tzystuck, 124 Ill. 2d at 238.) Because the defendants in Tzystuck could not reasonably be surprised that the treating physician was rendering an opinion about the plaintiff’s medical condition, disclosure under Rule 220 was unnecessary.
As additional support for the holding in Tzystuck, this court noted that a party cannot exert the same control over a nonretained expert that can be exerted over a retained expert. This was significant because of the discovery requirements Rule 220(c) imposes on the party retaining an expert witness. While the lack of control bolsters the rationale of the holding in Tzystuck, we believe the primary basis of the decision rests in the need to eliminate surprise expert testimony.
Since Tzystuck was decided, our appellate court has been called upon to determine whether various experts were “retained” under Rule 220. In each instance, the appellate court has examined the expert’s relationship to the case to determine whether the expert’s opinion testimony would surprise the opposing party. See, e.g., Nolan v. Elliott (1989), 179 Ill. App. 3d 1077 (former ambulance driver who was eyewitness to accident involving ambulance was Rule 220 expert for purposes of testifying regarding proper procedures to be followed by ambulance driver on emergency run); Smith v. Central Illinois Public Service Co. (1988), 176 Ill. App. 3d 482 (engineer employed by defendant as plant manager is not Rule 220 expert in case involving design and construction of facility at which plaintiff injured); Redmon v. Austin (1989), 188 Ill. App. 3d 220 (fireman present at scene after an auto accident was Rule 220 expert for purposes of reconstruction testimony); Voyles v. Sanford (1989), 183 Ill. App. 3d 833 (assistant driver of truck involved in accident was not Rule 220 expert for purposes of giving opinion on proper braking procedures for truck).
We agree with our appellate court that the question of whether a witness must be disclosed as an expert under Rule 220 depends on the expert’s relationship to the case. If the expert is intimately involved in the underlying facts giving rise to the litigation and he would reasonably be expected to form an opinion through that involvement, then disclosure is not required. In such a case, the opposing party is unlikely to be surprised by the testimony. On the other hand, where the expert’s contact with the case is slight, or where the opinion rendered is unrelated to the expert’s involvement in the case, then disclosure is required.
In the present case, we find that because Lahlien’s testimony was beyond the scope of his investigation, he was a “retained expert” under Rule 220. Lahlien’s role as the investigating officer was limited to identifying and apprehending the man who shot plaintiff. Due to his status as a post-occurrence witness, Lahlien could testify regarding the facts uncovered by the investigation without the need for disclosure under Rule 220. (See Redmon, 188 Ill. App. 3d at 226.) However, Lahlien could not give his opinion regarding matters unrelated to his investigation without disclosure.
Lahlien testified that in his opinion the Ramada Inn was not located in a high-crime area and that there was no need for a security guard at the hotel. These opinions are unrelated to his investigation of the underlying crime in this case. But for the litigation Lahlien would not have been called upon to render an opinion about the need for a security guard. The opinion is not so related to the investigation of the crime that a party could reasonably anticipate that Lahlien would testify on the matter. Thus, even though Lahlien investigated the crime independently of plaintiff’s lawsuit and was not under defendant’s control, he was a retained expert under Rule 220.
We also reject defendant’s argument that any error in the admission of Lahlien’s testimony was harmless. Defendant contends that Lahlien’s testimony was cumulative of the testimony of defendant’s other expert. However, given Lahlien’s status as investigating officer, we cannot presume that his testimony had no impact on the jury’s decision. Therefore, we find the error was not harmless.
Because we affirm the appellate court’s decision on this issue, we need not consider defendant’s other arguments on appeal.
For the foregoing reasons, we affirm the appellate court’s judgment.
Affirmed.