I recall that all of the White House security cameras went down that day, so there was no evidence of anyone’s comings and goings.
The White House campus has possibly the most extensive security of any piece of real estate in the world. So the chances all of the White house security cameras being down on the day of Vince Foster's death are as remote as the chances that the 9/11/12 Benghazi attack on the American facility was precipitated by an Internet video.
But the government claim that the White House security cameras were down is an important clue in and of itself. That's because IF Foster drove himself in his own car from the White House campus to Fort Marcy Park to commit suicide there, which is the official government story, the government would have gladly released the video security camera footage of the Foster Honda leaving the premises shortly after noon on the fatal day. And it may have also released security footage of Foster's car entering the premises earlier in the morning. That's because we know from reliable eyewitness statements that he was indeed on the White House premises on foot early that morning and was last seen there on foot shortly after noon. The absence of visual (or any other) evidence of Foster's vehicle ever being anywhere on the White House campus that morning while he himself was there pretty much debunks the "he-drove-himself-to-the-park-and-committed-suicide-there" theory because he seemingly had no access to the car that he allegedly drove to do that! There is no documentation that the Foster Honda ever arrived at the White House that particular day, in contrast to just about every workday since he arrived in Washington.