Detective Superintendent Raymond Murray said that the bomb that killed Constable Kerr was held in a plastic container, a similar size to a lunchbox. He also said that it was likely set off by a tilt switch, which activated the bomb when the car moved.
Chief Supt. Murray said the bomb was likely to have been planted sometime between Thursday night and when it exploded Saturday afternoon.
He described the murder of Constable Kerr as "grotesque" and "brutal."
No group has yet claimed responsibility for the bombing, and Chief Supt. Murray would not speculate on which group was responsible.
Police have appealed to anyone who was in the Highfield area of Omagh between Thursday and Saturday to come forward with any information, no matter how small or insignificant a detail it may seem.
For more, click over to BBC Northern Ireland.