An independent report that found serious police and government failures in responding to violence at a white nationalist rally in Charlottesville this summer also accuses police agencies of putting up roadblocks to the investigation.

The report, released on Friday by former US attorney Tim Heaphy, said Virginia state police refused to make commanders on the ground at the 12 August rally available for interviews or to provide most documents requested. It also said the Charlottesville police chief, Al Thomas, deleted relevant text messages and made officers fearful of retaliation for speaking with investigators.

Thomas’s lawyer denied texts were deleted. He spoke at a news conference in which community activists peppered Heaphy with questions and shouted at Thomas, illustrating the deep distrust between some Charlottesville citizens and law enforcement officials after white nationalists descended on the Virginia city over its decision to remove a Confederate monument.

“We are a community divided. We are still a community in crisis,” Thomas said.

The report’s findings come a little over three months after the rally, which was believed to be the largest gathering of white nationalists in at least a decade. Street fights erupted between white nationalists and counter-demonstrators before the event officially began, and the brawling lasted nearly an hour in view of officers until authorities forced the crowd to disband.

Later, as counter-demonstrators were peacefully marching downtown, a car drove into the crowd, killing 32-year-old Heather Heyer and injuring many more.

Heaphy’s report was sharply critical of Thomas’s response as the violence began to escalate that day. According to the report, as brawling first broke out, Thomas said: “Let them fight, it will make it easier to declare an unlawful assembly.”

Thomas did not recall making that statement, which was cited in accounts by two other police employees, though he confirmed he waited to “see how things played out” before declaring an unlawful assembly, the report said.

“Chief Thomas’ slow-footed response to violence put the safety of all at risk and created indelible images of this chaotic event,” it said.

The report also said Thomas initially tried to limit access to certain information by directing subordinates not to answer certain questions. And it said Thomas and other Charlottesville police command staff deleted text messages relevant to the investigation.

Kevin Martingayle, an attorney for Thomas, said the chief disputes that.

White nationalist demonstrators clash with counter-demonstrators at the entrance to Lee Park in Charlottesville, Virginia, on 12 August. Photograph: Steve Helber/AP

Heaphy, now in private law practice, said he eventually got the information needed from city police, but that was not the case with Virginia state police. Virginia’s secretary of public safety and homeland security, Brian Moran, was initially willing to cooperate, Heaphy said, but Moran’s office later invoked executive privilege over certain information amid concerns about possible litigation against the state.

State police allowed Heaphy’s team to interview the agency’s leader and two troopers not present on 12 August. But the report said state police refused requests to interview four others “important to our evaluation” and turned over just one document.

Heaphy’s team, however, said it obtained a second document, a detailed plan for state police resources on 12 August, after copies were accidentally left behind in a staging area.

Moran and state police spokeswoman Corinne Geller did not respond to requests for comment.

The investigation – which involved about 150 interviews and a review of photos, video and more than half a million documents – found a lack of coordination between state and city police and a passive response by city officials to the chaos. The report also found police removed an officer from the area where the car smashed into counter-demonstrators, leaving only a small sawhorse in place at the time.

The report also said the fact that officers were dressed in everyday uniforms, not riot gear, at the outset of the day caused problems. Their helmets and shields were staged behind barricades, not beside officers, Heaphy said, requiring them to leave conflict areas to retrieve that equipment.

“Supervisors devised a poorly conceived plan that under-equipped and misaligned hundreds of officers. Execution of that plan elevated officer safety over public safety,” the report said.