The investigation continues into the tragic killing of an on-duty Oakland police officer last week who was among several officers responding to an alleged cannabis dispensary burglary. And over the holiday weekend, the OPD says it made "several" arrests.

"In collaboration with our law enforcement partners, OPD has made significant progress in the investigation, resulting in several additional arrests over the weekend," the department said in a press statement Tuesday. "This is just the beginning of a lengthy legal process; we are hopeful that it will start the healing for Officer Le's grieving family and our entire OPD family."

"We are all devastated by this senseless act of violence, and our hearts continue to mourn his passing," the statement added.

According to the department, one of the arrests just occurred in the last 12 hours, but the suspects have not been named.

The shooting happened early in the morning on December 29, and plain-clothed officer Tuan Le was fatally shot, while another officer was shot and sustained an injury. According to Oakland police, the officers did not fire on the suspects, but were themselves fired on in an ambush-style shooting, after they began to pursue the suspects believed involved in the second burglary at the same location that same night.

The location was near Jack London Square and Oakland's Embarcadero, and the dispensary has not been publicly named.

Le, who had been with the OPD for just shy of four years, was born in Vietnam and became a naturalized U.S. citizen on Sept. 11, 2001, as the Chronicle reports. He had been serving as a community resource officer in West Oakland for the past two years, according to the OPD.

It has remained unclear since Friday how many suspects were involved in the alleged burglary and shooting. Police said Friday that the suspects fired from a black vehicle.

Le was driving an unmarked vehicle at the time of the shooting — possibly the white Toyota Tacoma pickup truck that was seen crashed at the scene, riddled with bullet holes.

Officers rushed Le to Highland Hospital without waiting for an ambulance, but he was pronounced dead there at 8:44 a.m. Friday, about four hours after the shooting.

Oakland Mayor Sheng Thao said at a press conference later that day, "This loss cuts deep... This senseless murder of a police officer, one of the guardians of our beautiful city, it will not stand."

This was the first Oakland officer killed in the line of duty since 2009.

If you have any information on this incident, you’re asked to call the Oakland PD Homicide Unit at (510) 238-3821. Tipsters can remain anonymous.

Previously: New Details on Killing of OPD Officer: He Was a Four-Year Veteran, Shooting Was Over Dispensary Robbed Twice Friday