Pat Tillman taught his comrade in arms Russell Baer a couple of important things.

In life, Mr. Tillman, the football star who walked away from a multimillion dollar career with the NFL to go and fight for America, taught Mr. Baer not to prejudge people.

When he heard the star player was joining his unit, the second platoon, Alpha company of the second 75th Ranger regiment, for the invasion of Iraq, Mr. Baer expected him to be “some jock meathead” with a huge ego.

“But I was completely wrong in my assumptions,” said Mr. Baer yesterday, speaking about his friend and the movie about him.

First, Mr. Tillman was well-spoken and well educated, into all the same things Mr. Baer was into, like reading, poetry, politics.

“And he was completely non-egotistical. He was kind, he was accommodating. It didn’t matter who you were, he would always pull you into the conversation. It didn’t matter whether you were some rough-around-the-edges ex-gang-banger from Philadelphia, you were welcome at the table.

“He was different from anybody I’d ever met. Strong, strong in his beliefs. It just seemed like he got it. Like he got life. He and his brother seemed to have something that was missing in my life and the general populace,” Mr. Baer said.

They became friends in Iraq, and deepened their friendship in Afghanistan.

In death, Mr. Tillman taught him something far darker. That all those concepts, “like honor and honesty, service and sacrifice” which were drummed into lowly recruits meant nothing to political and military elites intent on propagandizing war.

Now, the tragic death of Pat Tillman and spin and outright lies which followed it have become a movie, The Tillman Story. And Mr. Baer, at the request of the dead soldier’s family, is coming to the Vineyard to present it.

For those unfamiliar with the case, Pat Tillman was caught in a fire fight in Afghanistan and killed on April 22, 2004.

The military and political establishment immediately designated him a hero, awarded him the silver star and posthumously promoted him. The story was that he died heroically fighting the Taliban. The reality was that he was a casualty of “friendly fire” as they euphemistically call it when troops are mistakenly shot at by their own side.

But the reality was of no concern, apparently, when Mr. Tillman’s death could be used as a recruiting tool.

In fairness, there was initial confusion about the cause of death. Mr. Baer, who was only about 20 feet from his friend when it happened, was not sure himself. There was an ambush, the Taliban were shooting, their guys were shooting, and while he was pretty sure Mr. Tillman was hit by an American bullet, he could not be sure.

Worse, it was another part of their own force who were shooting at them. Worst case, Mr. Tillman’s brother, Kevin, who was with them, might have fired the fatal shots.

And so when Mr. Baer and Kevin accompanied the body on the flight home, they hardly exchanged a word. Although Mr. Baer knew by then it had not been Kevin, who, it transpired, had been in the second half of the convoy and did not see the action, he still did not know which side shot his friend. When Mr. Baer met the parents, he did not know what to say.

“Who wants to be the guy who says, yeah, it was friendly fire, and then they find AK47 rounds in him? How could I put a family through that kind of turmoil?”

And so at first, when they realized there had been a cover-up, the family was angry at Mr. Baer too. They thought he had been part of it.

“The father thought I’d blatantly lied to them,” he said. “But now the family understands the position I was in.”

The confusion was hard enough to bear, the knowledge that the people at the top had then gone on to perpetuate an untrue version of events was, in the end, unbearable.

Mr. Baer stayed in the Rangers for one more tour of Afghanistan, but his perception of the military had soured.

“I planned possibly to make it a career, but I got out in March 2005. I got out running, because I really felt betrayed by the military system itself.

“When you go in, you’re re-raised in the military, to believe in things like honor and honesty, service and sacrifice. The experience of Pat’s incident really showed me just how people in the higher echelons of the military and the government would tell you one thing and do another.

“It left a really sour taste in my mouth. And there were lots of stories about guys getting out who were just not being taken care of. Veterans coming home, messed up, and not cared for by the government, the VA [Veterans’ Affairs] system.”

Since then, he’s worked in personal security, while studying filmmaking. Not that he had much to do with the making of The Tillman Story.

“They sourced me for various gaps in their information, I helped them out by contacting other people who knew relevant things, but that’s about it,” he said.

As for the finished product, he said there were some discrepancies between his understanding of events and those in the film. But only minor ones.

“I’m happy with it and the family’s happy with it,” he said.

“What I liked about the way the director, Amir Bar-Lev, did it was that he did not make it overtly political. I didn’t want to be a part of anything that was too political, and nor did the family. They stuck with the facts of the situation.”

As for the war which claimed his good friend’s life, Mr. Baer still thinks it rightly entered, although badly prosecuted.

He joined the second battalion on Sept. 10, 2001, the day before the attack on the World Trade Center, “and I was over in Afghanistan about three months later.”

But he found the U.S. war effort was disjointed and ineffective.

“I was raised in a military family, and you expect certain things to happen when you invade. But on that first deployment we pretty much sat in the hills and watched the enemy leave the country, into neighboring Pakistan,” he said.

“I believe we should be over there. I believe war is never right, but it is sometimes necessary. But in my opinion they are only now starting to do what they should have been doing at the beginning.

“There were some very bad decisions made during the previous administration,” he said.

“I think this is a conflict . . . that I don’t see ending in the next five years. I could see us being there for the next 20,” he said.

The film will screen at 8 p.m. Wednesday at the Chilmark Community center, as part of the Martha’s Vineyard Film Festival. Mr. Baer will be available afterwards to field questions about his friend and the two wars in which they fought.