Constable Kerr, 25, died when a bomb exploded under his car at Highfield Close in Omagh in April 2011.
Detectives are also trying to identify 11 vehicles and one man in the vicinity of Highfield Close in the days leading up to the murder and on the day itself.
Police have said they could be valuable witnesses or suspects.
They have put a map of the murder scene and the vehicles on the PSNI website.
Detective Superintendent Raymond Murray said the police investigation had Constable Kerr’s murder at its core, but included several linked incidents.
These included an arms find, attempted murders, armed robberies and a number of other terrorist attacks.
“We are 10 months into this investigation but there is a long way to go,” Det Supt Murray said.
“We have trawled through an enormous amount of information obtained from our enquiries and material gleaned from previous appeals.
“But there are still gaps which we are endeavouring to close in terms of building up a complete picture of the events leading up to the explosion.
“To date, there have been 56 searches, 10 arrests and one person charged as part of the overall investigation.”
Anyone with information is asked to contact detectives on 028 8225 6687
Ronan Kerr murder: Graffiti lauding bomb ‘disgusting’
The slogans were painted in the Bogside estate, an area with a predominantly republican population.
One read: “GAA cops, look what use (sic) got”. It refers to Constable Kerr’s membership of a Gaelic football club.
The graffiti is being painted out and has been condemned by politicians.
Constable Kerr, 25, was killed when a booby-trap bomb exploded underneath his car in Omagh, County Tyrone on Saturday afternoon.
Dissident republicans have been blamed for the attack.
They are opposed to the police and have repeatedly targeted officers in both gun and bomb attacks.
They are believed to be deliberately targeting Catholic officers in order to try to deter Catholics from joining the PSNI.
Last year, Peadar Heffron, a Catholic officer who played for the PSNI Gaelic football team, lost his legs in a similar booby-trap bomb attack.
Outgoing SDLP MLA Pat Ramsey said that it was the second day that such “despicable and disgusting” slogans had appeared.
He added: “People really are outraged by this.
“This is not indicative of the feeling among the people of the Bogside and that is why those responsible skulked around in the dark of night and did their deed.
“They are not standing up and saying it, they are using the same cowardly tactics of those who callously murdered Pc Kerr.
“The people of the Bogside are angry this morning, they have been angry since Saturday, just like the rest of the north.
“They do not deserve to be tarnished with this and the good name of PC Kerr does not deserve to be tarnished like this.”
WITH MANY THANKS TO BBC NEWS
- Kerr murder: Appeal over 11 cars (bbc.co.uk)
- Stephen Carroll trial: Army ‘reluctant to hand over device’ (seachranaidhe1.wordpress.com)
- Ex-Sinn Fein Man On Trial Over Police Murder (seachranaidhe1.wordpress.com)
- “This is a read-back into the so-called ‘dirty war’…” (sluggerotoole.com)