Denver police launched an internal investigation into a family's claim that four police officers beat a 17-year-old boy for 15 to 20 minutes for no apparent reason, a department spokesman said today.

A dozen family members demonstrated Wednesday at the edge of Civic Center to complain about the alleged beating of John Crespin on Jan. 20 in the 600 block of Perry Street.

"My son was coming home after taking family photos at the flea market," said the teen's mother, Delilah Quintana, 36, of Denver. "The police followed him to our house and then repeatedly beat my son for 15 to 20 minutes in the driveway of our home as we watched helplessly. They had no motive and no probable cause for doing so."

Crespin, 17, was arrested and charged with assaulting a police officer and remains in the Gilliam Youth Detention Center, family members said.

Crespin's family has filed a notice of intent to sue the police department.

Denver police spokesman Sonny Jackson said he could not comment about the incident because it involved a juvenile. Family members who witnessed the incident gave this account:

Around 2:15 p.m. Jan. 20, Cres pin was followed home by police after he and his girlfriend saw four officers arresting and beating up two young boys along Osceola Street, a block from Perry Street.

Police ordered Crespin to get out and place his hands on his car. When he complied, witnesses said, police kicked his legs out from under him, placed him in a chokehold and started hitting him with billy clubs and nunchucks, blackening his right eye and leaving 18 bruises and marks on his body.