The Stranger You Know by Jane Casey

The latest crime thriller featuring detective Maeve Kerrigan - winner of the Mary Higgins Clark Award
He meets women.
He gains their trust.
He kills them.
That's all Maeve Kerrigan knows about the man she is hunting. Three women have been strangled in their homes by the same sadistic killer. With no sign of a break-in, every indication shows that they let him in.
But the evidence is pointing at a shocking suspect: DI Josh Derwent, Maeve's colleague.
Maeve refuses to believe he could be involved, but how well does she really know him? Because this isn't the first time Derwent's been accused of murder...