In this case, a police officer stopped a car late at night. Because the car was traveling below the posted speed limit, the officer suspected the driver of being intoxicated. The day after the stop, police discovered that the driver and his passenger (the defendants in this case) had been traveling in a car owned by a woman who had been murdered shortly before the stop. The majority upholds the legality of the detention. I disagree.
I
Around midnight on March 1, 1988, Visalia Police Officer Alan Wightman saw a Ford Fairmont traveling through downtown Visalia. It had rained heavily in that area a couple of hours earlier; parked cars in the area were wet, while many moving vehicles were dry because the drops had blown off. Because the Ford Fairmont’s exterior was wet, Officer Wightman suspected it had been parked nearby until recently. In the previous three months, the *217police had received many reports of vehicle theft and vehicle tampering at approximately 10 used car lots in downtown Visalia. A week earlier, one of the lots, which the officer described as a “used Ford car lot,” had reported a car theft. Suspecting that the Ford Fairmont might be stolen, Wightman followed the car as it traveled through town (breaking no laws) and turned onto an on-ramp to State Highway 198, on which no other cars were traveling at the time. A call-in by Wightman soon revealed that the car was owned by a private party, Ivon Pontbriant, and that it had not been reported stolen.
At the point where the car entered State Highway 198, it was a freeway, with a maximum speed limit of 55 miles per hour. But after a very short distance, which Officer Wightman estimated at “a half, three quarters of a mile, closer to a mile maybe,” it became a highway with a maximum speed limit of 45 miles per hour. The car traveled at 40 miles per hour on the short stretch of freeway; the officer then stopped the car where the speed limit dropped. He did so primarily because he suspected the driver of being intoxicated, explaining that in his experience intoxicated drivers tend to drive slowly for no apparent reason.
In the car were defendants Richard Lacy Letner (the driver) and Christopher Allan Tobin (the passenger). Letner told Officer Wightman that he had borrowed the car from Ivon Pontbriant; Letner and Tobin, who was drunk, made inconsistent statements regarding their destination. Officer Wightman patted down Letner and found a buck knife in his pants pocket; he also saw an opened beer bottle in plain view in the car. When Letner could not produce a license, Officer Wightman ordered the two defendants to walk home.
The next day, after learning of Pontbriant’s murder, police officers searched the car and found, in addition to personal property belonging to both defendants, a rag with blood on it consistent with defendant Tobin’s. At Pontbriant’s house, the police found beer bottles of the same brand as the opened bottle that Officer Wightman had seen in the car at the time of the stop the previous night.
H
“[L]aw enforcement agents may briefly stop a moving automobile to investigate a reasonable suspicion that its occupants are involved in criminal activity. [Citation.] Although stopping a car and detaining its occupants constitute a seizure within the meaning of the Fourth Amendment, the governmental interest in investigating an officer’s reasonable suspicion, based on specific and articulable facts, may outweigh the Fourth Amendment interest of the driver and passengers in remaining secure from the intrusion. *218[Citation.]” (United States v. Hensley (1985) 469 U.S. 221, 226 [83 L.Ed.2d 604, 105 S.Ct. 675].) Here, as explained below, at the time of the car stop Officer Wightman lacked a reasonable suspicion that defendants were involved in criminal activity.
That the car, while being followed by a marked police car, was traveling 15 miles per hour below the maximum speed limit of 55 on State Highway 198, did not give rise to a reasonable suspicion that the driver had stolen the car and was therefore trying to avoid contact with the police: It is not at all unusual for a driver to slow down upon seeing a police car, irrespective of any wrongdoing. Here, the driver did not suddenly slow down when Officer Wightman began following the car. Rather, the driver merely did not accelerate to the maximum speed limit after entering the freeway.
Four reasons come to mind as to why, under the circumstances of this case, a driver might have driven slowly on the freeway. First, if, as Officer Wightman testified, parked cars in downtown Visalia were still wet from a recent heavy rain, it is reasonable to infer that the freeway too was still wet, which would lead most motorists to slow down because of slippery road conditions.1 Second, it is not at all unusual for drivers not to accelerate to a maximum speed limit when, as here, they can drive at that speed only for just about a mile before a drop of the posted speed limit. If defendant Letner, instead of driving at 40 miles per hour on the freeway, had immediately accelerated to the maximum speed limit of 55 miles per hour after entering the freeway, he could have maintained that speed only for a minute before the speed limit on the stretch that became a highway fell to 45 miles per hour. Third, the stop occurred at midnight; many people drive slower late at night, because of poor visibility. Fourth, Officer Wightman testified that the car’s engine was “running rough”; a driver experiencing that problem might fear a mechanical problem and decide not to drive at the maximum posted speed limit.
Although there is no published California decision on the legality of stopping a car simply because it is traveling below the maximum speed limit, courts in other states have concluded that such a stop lacks the requisite reasonable cause to believe that the driver is engaged in criminal activity unless there are other suspicious circumstances. (See Faunce v. State (Fla.Dist.Ct.App. 2004) 884 So.2d 504, 506 [“the fact that the defendant in this case was driving slowly is not alone sufficient to give rise to a reasonable suspicion”]; State v. Brown (N.D. 1993) 509 N.W.2d 69, 71 [“The mere fact *219that a driver is traveling at a slower than usual speed on a roadway does not by itself create a reasonable suspicion of driving under the influence of alcohol or of other illegal activity.”]; State v. Bacher (2007) 170 Ohio App.3d 457 [2007 Ohio 727, 867 N.E.2d 864, 867]; State v. Rincon (2006) 122 Nev. 1170 [147 P.3d 233, 236-237]; Richardson v. State (Tex.Ct.App. 2000) 39 S.W.3d 634, 640; Raulerson v. State (1996) 223 Ga.App. 556 [479 S.E.2d 386, 387]; People v. Rotkvich (1993) 256 Ill.App.3d 124 [195 Ill.Dec. 424, 628 N.E.2d 888, 892]; see also U.S. v. Diaz (5th Cir. 1992) 977 F.2d 163, 165; U.S. v. Abdon-Limas (D.N.M. 1991) 780 F.Supp. 773, 780.) Here, there were no suspicious circumstances tending to show that the occupants of the car were engaged in illegal activity.
Because of the recent rain, Officer Wightman found it significant that droplets of water were still on the car. This led him to suspect that the car had been stolen from one of the car lots in downtown Visalia. At most, however, the presence of raindrops on the car indicated that it had not been driven a long distance. It did not indicate that the car had been stolen from a carlot; the car could have been parked in the downtown area before it was driven to the freeway. And once Officer Wightman learned, before stopping the car, that it was registered to a private owner rather than a car dealer, it was no longer reasonable for him to believe that the car had been stolen from a carlot.
According to the majority, however, Officer Wightman reasonably suspected the car was stolen from a car lot in downtown VisaHa. To explain why this suspicion was reasonable even after Officer Wightman learned that the car was owned not by a car dealer, but by a private party (Pontbriant), the majority asserts that “the dealer might have recently purchased [the car] and not yet updated the ownership records, or the car could have been at the dealership for repairs.” (Maj. opn., ante, at p. 148.) These hypothetical assertions are too speculative to support the majority’s conclusion of reasonable suspicion by the officer that the car had been stolen from a car lot.
The majority also cites three cases to support its conclusion that, because the car in question was traveling 15 miles per hour below the maximum speed limit of 55, “a reasonable officer might suspect the driver of the car was attempting to avoid contact with the police.” (Maj. opn., ante, at p. 147.) These three cases are distinguishable, however.
The first case, U.S. v. Villalobos (5th Cir. 1998) 161 F.3d 285, states that “noticeable deceleration in the presence of a patrol car can contribute to reasonable suspicion, even though drivers often slow when they see law enforcement personnel.” (Id. at p. 291.) But here the car did not decelerate-, rather, it merely failed to accelerate to the maximum 55-mile-per-hour speed limit when it entered the freeway.
*220The second case, U.S. v. Lopez-Martinez (10th Cir. 1994) 25 F.3d 1481, states that “maintaining a noticeably slow speed in the presence of a police officer may suggest nervousness . . . (Id. at p. 1486.) But in that case two cars were both traveling near the Mexican border, at a speed far below the posted speed limit (30 miles per hour when the posted speed limit was 55 miles per hour) in broad daylight and in good weather, when no other cars were on the road; there was no apparent explanation for the cars’ slow speed. Here, the car driven by defendant Letner was going significantly faster (40 miles per hour in a 55-mile-per-hour zone) when stopped and, as explained earlier (see pp. 218-219, ante), the circumstances surrounding the stop indicated that the car was traveling at that speed for valid reasons.
The third case on which the majority relies is People v. Gibson (1963) 220 Cal.App.2d 15 [33 Cal.Rptr. 775], which states: “The fact that a driver proceeds at a speed slower than the speed limit under circumstances where he might normally proceed at the higher speed also is a factor appearing to justify an officer’s investigation.” (Id. at p. 20.) But in Gibson the detaining officers observed the slow-moving vehicle within two minutes after learning of a robbery on the same street, at a time (4:00 a.m.) when no other cars were on the street; while following the car, the officers “observed a motion . . . which looked to them like ‘someone was trying to put something in the back part of the car’ or ‘someone moving something in the car.’ ” (Id. at p. 18.) Such facts are lacking here.
When, as in this case, a trial court erroneously denies a motion to suppress evidence obtained in violation of the federal Constitution’s Fourth Amendment, the error is harmless only if the reviewing court can say “beyond a reasonable doubt that the evidence complained of did not contribute to” the conviction. (Franks v. Delaware (1978) 438 U.S. 154, 162 [57 L.Ed.2d 667, 98 S.Ct. 2674]; see also Bumper v. North Carolina (1968) 391 U.S. 543, 550 [20 L.Ed.2d 797, 88 S.Ct. 1788].) Here, Officer Wightman’s midnight observation of both defendants in a car that belonged to Ivon Pontbriant, together with evidence indicating that Pontbriant was murdered earlier that night, played a key role in the prosecution’s case. Although the prosecution also presented other evidence tending to show guilt, I cannot say beyond a reasonable doubt that Officer Wightman’s testimony did not contribute to the jury’s verdict.2
*221For the reasons given above, I would reverse both defendants’ murder convictions and judgments of death.
Appellants’ petition for a rehearing was denied September 15, 2010. Kennard, J., was of the opinion that the petition should be granted.
A handbook for California drivers published by the California’s Department of Motor Vehicles recommends that motorists reduce their speed by five to 10 miles per hour on wet roads. (Dept. Motor Vehicles, 2010 Cal. Driver Handbook (2010) p. 67 <http://www.dmv.ca.gov/pubs/ dl600.pdf> [as of July 29, 2010].)
Justice Werdegar’s concurring and dissenting opinion agrees with me that Officer Wightman’s detention of defendants was illegal. But she concludes that certain evidence found in the car linked defendants to the murder and was admissible against defendants notwithstanding the illegal detention. She reasons: “[B]ecause neither defendant owned or legitimately possessed the car in which this evidence was found, they are foreclosed from challenging the legality of *221the car’s search.” (Cone. & dis. opn. of Werdegar, J., ante, at p. 213.) Based in part on this conclusion, she reasons that the trial court’s erroneous denial of defendants’ motion to suppress the seized evidence was harmless beyond a reasonable doubt. I disagree.
I do agree that defendants are foreclosed from challenging the legality of the car search, because the car was not owned by defendants but by murder victim Pontbriant. But at issue here is not the legality of the search; at issue here is the legality of the detention that preceded the search. “If the physical evidence found in the vehicle[] was the fruit of the defendants’ unlawful detention, it must be suppressed,” even though the defendants lacked a possessory interest in the vehicle. (U.S. v. Shareef (10th Cir. 1996) 100 F.3d 1491, 1499-1500; see also 6 LaFave, Search and Seizure (4th ed. 2004) § 11.3(e), pp. 194-196; People v. Glick (1988) 203 Cal.App.3d 796, 799-800 [250 Cal.Rptr. 315].) Here, the seizure of the evidence linking defendants to the murder followed Officer Wightman’s illegal detention, after he ordered both defendants to leave the car, which still contained the incriminating evidence, by the road. Thus, that seizure was a fruit of Officer Wightman’s illegal detention of defendants (see Wong Sun v. United States (1963) 371 U.S. 471, 487-488 [9 L.Ed.2d 441, 83 S.Ct. 407]), and the items found in the car should have been suppressed.