Tony Vera Echevarria / YouTube

A young man with a snare drum immediately before he strikes an LAPD officer

DOWNTOWN LOS ANGELES — Two LAPD officers were injured in Downtown's May Day rally this week, and police are hoping that video taken of the incidents may help them track down the suspects. In one case, it already has.

The footage was captured by Tony Vera Echevarria, a photographer and documentary journalist who has been living in Venice Beach for the past 20 years, according to his website.

In one video, a young man with a drum is shown coming up from behind a female officer and hitting her in the back of the head with it.

The officer was struck so hard it broke her Kevlar helmet, which is used to help stop bullets, officials said to blogdowntown. She suffered a semi-concussion and is now at home resting according to LAPD Chief Charlie Beck who spoke to media Wednesday.

A protester who was at the march saw the video on YouTube and called police to alert them to the footage of the attack, said Capt. Horace Frank. A few LAPD officers recognized the man in the video as someone they had arrested a few weeks prior. They were able to track him down Wednesday and arrested the suspect on suspicion of felony assault on a peace officer

"That video was extremely helpful," Frank told Blogdowntown. "There's no doubt about that."

The L.A. Times reports that the suspect is Brian Mendoza, 23, known to frequent Skid Row and is on probation for a previous attack on an officer in El Monte.

In another video by Echevarria, officers are shown being hit from behind with a large wooden palette. Two men dressed in black are holding the item and are seen standing behind the officers before rushing them from the back. After the impact, the officers flip around and begin swinging their batons.

CBS reports that Echevarria has been covering protests since the beginning of Occupy L.A., and he said what he witnessed on Tuesday turned his stomach.

“It was a sucker punch from behind with a futon board. One cop fell, back of his head, it was ugly,” Echevarria told CBS.

Police are still looking for the men in this attack. Other than these two incidents, Beck said it was a mostly peaceful march.

"There were thousands of people that did this the right way and they got their message across and individuals like this detract from that," Beck said at the LAPD headquarters.