The San Francisco Police Department is seeking a suspect in a bizarre, seemingly unprovoked attack that left a popular Tenderloin man seriously injured.

You can see the attack in the video below, but I'll warn you, it's disturbing. In the footage, released by the SFPD Thursday, you can see Robert, a homeless man who's lived on the streets of the Tenderloin for years. It's 9:30 Wednesday night, and he's sitting in one of his usual spots, a stool outside The Gangway, a bar located at 841 Larkin Street near Geary Street.

Suddenly, a guy wearing a blue shirt walks toward Robert and hits him in the head with what appears to be a metal pipe, rod or bat. The blow was so forceful that the weapon was knocked out of the assailant's hand.

Robert fell to the ground, seriously injured, as the man retrieved his weapon and strode off.

SFPD spokesperson Officer Carlos Manfredi, who used to be a Tenderloin beat cop, told ABC7 that he's taking the attack personally.

"He's a very nice man. He doesn't try to harm anyone. He always says hi to everyone who says hi to him," Manfredi said.

“He always had a smile on his face. No matter how bad the situation, or no matter how bad the weather is, or how hungry he could’ve been,” Manfredi told KPIX.

According to KPIX, "police believe the attack was planned because cameras captured the suspect casing the scene," some of which you can see in the video below.

Jung Lee, owner of The Gangway, says that he cleaned up Robert's blood after the attack.

"The Robert victim, he's a regular guy...He sit here morning, day, night. You know, every day, maybe a decade, 10 years," Lee said.

According to a police spokesperson, they do not believe that the attacker is homeless, and are hopeful that someone will see the video and contact police with his identity.

Of course, this isn't the first beating of a homeless person that's been caught on tape, nor the only one where the suspects, as yet, remain free. On November 23, 2014, a group of three men were caught on tape as they kicked and beat Tai Lam to death as he slept in a Financial District alley. Though police circulated photos from the surveillance video, so far no arrests have been made.

However, Manfredi is holding out hope that this case is different.

"When you see an act so blatant and so raw, like this, it's uncalled for. In San Francisco we want to send a message to everybody who lives in the city or visits the city, if you attack the homeless, there's going to be a consequence," Manfredi told KTVU.

"We want to send a strong message to anyone who thinks it's OK to do this. If we catch you, you will be incarcerated."