Robert Bennett said Justine Damond was in her pyjamas when she approached them and "was not a threat to anyone".
Ms Damond was shot after approaching two officers in their car on Saturday after reporting a suspected rape.
Mr Bennett has acted in similar cases, including the high-profile police shooting of Philando Castile in 2016.
Fred Bruno, the lawyer for Matthew Harrity, whose partner killed Ms Damond, 40, had said: "It is reasonable to assume an officer in that situation would be concerned about a possible ambush."
But Mr Bennett told CBS News: "I think that's ludicrous. It's disinformation. It doesn't have any basis in fact."
He added: "She obviously wasn't armed, was not a threat to anyone, and nor could she have reasonably been perceived to be."
Officer Mohamed Noor, who shot Ms Damond in the abdomen in an upmarket neighbourhood of the city, has refused to be interviewed by investigators, as is his legal right.
Officer Harrity has spoken to investigators with the state's Bureau of Criminal Apprehension, which is leading the investigation.
On Thursday, a statement from Ms Damond's family said: "All we want to do is bring Justine home to Australia to farewell her in her hometown among family and friends.
"We are still trying to come to terms with this tragedy and we are struggling to understand how and why this could happen."
On Wednesday, police released the transcript of two separate 911 calls Ms Damond made after hearing screams nearby.
"I'm not sure if she's having sex or being raped," she told the police operator, before giving her address.
"I think she just yelled out 'help', but it's difficult, the sound has been going on for a while," she continued.
Ms Damond called back eight minutes later to ensure police had the correct address.
Body cameras, which are worn by all Minneapolis police, had not been turned on at the time of the shooting and the squad car dashboard camera also failed to capture the incident.
Officers Harrity and Noor, who between them have spent three years on the police force, have been placed on paid administrative leave.
Mr Bennett represented Philando Castile's family in pursuing compensation against the police.
Castile was shot by officer Jeronimo Yanez after his car was stopped, in an incident live-streamed on Facebook by his girlfriend.
Mr Yanez was acquitted of manslaughter and firearm charges but the family won $3m (Â£2.4m) in compensation.
A lawyer for the family of an Australian woman shot dead by police in Minneapolis says suggestions  officers feared an ambush were "ludicrous".