The widow and young daughters of Pc Dave Phillips have laid flowers at the scene where the Merseyside officer was mown down and killed by a stolen car.
Jen Phillips, 28, and her children Abi, seven, and Sophie, three, went to Dock Road in Wallasey as detectives announced that two women had been arrested on suspicion of assisting an offender, and two men were still being questioned about the murder.
Mrs Phillips and her daughters laid lilies at the scene where dozens of members of the public and police colleagues have already left their own floral tributes.
The parents of Pc Phillips, Robin and Carol, his youngest sister Kate, middle sister Hannah and her husband and their two children also visited the scene along with Jen's parents Robert and Kerry, and Jen's sister Rachel and her partner Anna.
The two female suspects, aged 19 and 34, and both from Wallasey, were detained last night hours after two men, aged 18 and 30, from the Oxton and Wallasey areas of the Wirral, were held in connection with the murder.
Pc Phillips, 34, died after he was sent to assist following a burglary at an estate agent in Birkenhead, where a red Mitsubishi pick-up was stolen just after 1am on Monday.
Following a police pursuit at about 2.08am, Pc Phillips and a colleague attempted to use a "stinger" device to stop the Mitsubishi Challenger L200.
The vehicle mounted a central reservation and headed directly at the officer before speeding off.
Pc Phillips was given CPR by colleagues at the scene but died a short time later at Arrowe Park Hospital on the Wirral. The pick-up was later found abandoned in Corbyn Street, Wallasey.