Eight bikers, including a police detective who was off-duty, have been arrested so far on charges ranging from criminal mischief to gang assault.
Commissioner Raymond Kelly says police are still investigating.
Alexian Lien was pulled from his SUV and beaten on the street in front of his wife and toddler on Sept. 29.
Police say the assault occurred after Lien and a biker bumped on the West Side Highway, and they forced the SUV to a stop. The driver fled, plowing over biker Edwin Mieses Jr.
A lawyer for the detective said Friday he will testify before a grand jury.
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