A 20-year-old man involved in a fatal collision which took the lives of two women on Anzac Day has been arrested and charged with numerous offences, SA's Police Commissioner says.

He was also charged with one count of causing harm.

The crash involved three cars at the intersection of Cross Road and Fullarton Road at Urrbrae, east of Adelaide, just after 1:30pm on April 25.

Witnesses described seeing a Volkswagen ute "flying through the air" from the second-storey window of a nearby home.

Commissioner Stevens visited the scene on the day and later described it as "absolute carnage and shocking to see".

The crash took the lives of highly regarded SA Police Chief Superintendent Joanne Shanahan, 55, and "kind and loving wife, mother, daughter and sister" Tania McNeill, 53.

Chief Superintendent Shanahan's husband Peter was driving the Holden SUV she was a passenger in at the time, but he escaped with non-life-threatening injuries.

The driver of the Volkswagen ute, Mr Kitt, was taken to the Royal Adelaide Hospital with life-threatening injuries.

SA Police said Major Crash Officers charged Mr Kitt with two counts of aggravated causing death by dangerous driving and one count of aggravated causing harm by dangerous driving.

He has been bailed to appear in the Adelaide Magistrates Court on July 8.

On Friday, his parents released a statement that described how they had been worried about their son's mental health in the days leading up to the crash.

Mr Kitt's parents said it was "impossible to find the words to describe the depth of our despair".

"We have only known our son, Harrison, to be a kind, responsible and compassionate young man," Andrew and Kathy Kitt said.

"Harry was not himself and his behaviour had become so uncharacteristic that just a short time before the accident, one of his friends had called us to express his concerns for Harry's welfare."

Joanne Shanahan's life to be celebrated

Commissioner Stevens said Chief Superintendent Shanahan would be remembered by her family in a service on May 8 at 11:00am.

"The funeral service will be held in a way that enables as many people as possible who knew or cared about Joanne or her family to be involved, and the South Australia Police will be playing its part as well.

"The hearse will be travelling from Joanne's home address along a specified route, so anyone who would like to come outside and pay their respects as the hearse travels that route will be able to do so."

South Australia has now had five double fatalities recorded on its roads in 2020, after a head-on collision killed two brothers on Victor Harbor Road on Saturday afternoon.