A cell phone video shows San Jose police officers repeatedly using batons and a Taser gun on an unarmed San Jose State student, including at least one baton strike that appears to come after the man is handcuffed, as they took him into custody inside his home last month.

The video, made by one of the student’s roommates without the knowledge of police, shows that force was used even though the suspect was on the ground, and apparently offering no physical threat to the officers. Several experts in police force said the video appears to document excessive — and possibly illegal — force by the officers. A police spokesman Friday said the department had opened a criminal investigation of the officers’ conduct, after police officials viewed a copy of the recording.

The confrontation arose as Phuong Ho, a 20-year-old math major from Ho Chi Minh City, was arrested on suspicion of assaulting another of his roommates. He faces pending misdemeanor charges of exhibiting a deadly weapon and resisting arrest. Ho admits picking up a knife as he argued with a roommate. He was not armed when police arrived.

Experts cautioned that the grainy, shaky video, a copy of which was obtained by the Mercury News last week from Ho’s lawyers, is difficult to view and may not depict critical actions by Ho that justify the response. Nevertheless, four of the six experts who reviewed the video at the request of the newspaper said it raises serious concerns.

“It takes me back to the day I saw the Rodney King video on TV,” said Roger Clark, a certified policing expert and a retired lieutenant with the Los Angeles Sheriff’s Department, where he served for 27 years.

San Jose Police Assistant Chief Daniel Katz, after being shown the video by the newspaper, said the department takes the matter “very seriously.”

The video shows police standing over Ho in a hallway of his house for more than two minutes. During that time, one officer strikes Ho with a metal baton more than 10 times — at times swinging it with both hands — while another officer leans in and uses his Taser gun. The Mercury News was unable to reach either officer seen using force during the incident, despite written requests sent both through department officials and their union.

The roommate who made the video, Dimitri Masouris, said he considered the police response unnecessary and excessive. The roommate sold the tape to Duyen Hoang Nguyen, the San Jose lawyer now representing Ho.

Among the issues noted by the outside experts:

Ho remains on the ground, moaning and crying, as he is repeatedly struck. He does not appear to offer significant resistance, suggesting the high level of force is not necessary.

The officer most visible in the sequence stands for much of the time in a casual posture, at one point with his legs crossed. He seems to show no concern that the situation is potentially dangerous — raising additional questions about why force was being used.