Blood on the Water by Anne Perry

Blood on the Water: A William Monk Novel - As Monk and one of his men, Orme, patrolled the Thames, a pleasure boat explodes before their eyes.  Working as fast as they can, along with other men on the river at the time, they save as many can. However, nearly 200 men and women die in the explosion.  The next day, Monk's superiors place the London Metropolitan Police in charge of the investigation instead of the river police.  Very quickly, the police have a suspect and try and convict the man.  However, during a separate investigation, Monk learns that the convicted man was no where near the boat and could have not set the explosives that caused the boat to sink.  His superiors recognizing that they made an error, charge Monk with re-investigating the incident.