police purjury question

I have a good friend who is facing dwi charges and am curious about what effect lying to a grand jury by his arresting officer would have on his case.
When the officer went to grand jury he stated that he had seen my buddy's truck crossing the intersection that he (the officer) was stopped at a high rate of speed,and that was the reason for initial contact,He then repeated the statement in DMV hearings.
What had actually happend was the officer was sitting in another bar parking lot across the street.My friend left the bar,drove into a box store paking lot,went back behind the store(a local shortcut)and out the other side of the lot.The Officer took the main road to get where he knew my friend was going (it is the only place the road leads to connect with a main street)
His dash camera came on as he rounded the intersection he said he was stopped at,taking a right turn at about 25mph, with top lights on. Then you can see my friends truck pulling out of the box store parking lot (after a complete stop)turning right and going down the road
By now he is aware he is being stopped and pulls over. He stops and is the recipiant of a DWI .12 BAC three drinks
My friend was never within 500 feet of the intersection where the officer states he had sped through,giving him cause for the stop. The video tape confirms this without a doubt. as does the officers audio tape talking to another officer after the arrest stating that he pulled him over after he came out of the parking lot.
I am curious whether the officers statement would be considered perjury, and what effect that could have on a trial.
Thankyou for your time

From what i've heard in the past, it's illegal for a cop to sit in the parking lot of a bar, and wait for people to leave so he can bust them. As far as the cop lying goe's, they are trained to lie,to do whatever it takes to make their case. In Illinois whatever they put in their written report is god's law and can't in any way be refuted. Go to a lawyer for a free consultation and see what they say. Although they wont tell you much until you come up with some cash.

Well, you can make this into a pretty long drawn out case, with a large court fee and then your friend would be convicted anyway if he was indeed provably drunk. It really doesn't matter in Illinois if you are a lawyer or a cop... these are folks whose word is taken as gospel... even when they are clearly lying and clearly violating ethics. And frankly I'd give them every opportunity to find any way to convict your friend if he was driving drunk... IN ILLINOIS it is dui for a reading of .8. If you must drink, don't drive.