This is a list of Mystery Thriller Series with Romantic Subplot.

Both protagonists (male and female) should be in law enforcement and work together to solve the crimes.

If that's not possible then at least one of the protagonists (preferably female) should be in law enforcement.

Law enforcement members include: FBI agent, criminal profiler, police officer, detective, police chief, sheriff, and so on.

The protagonists can even be in a related profession such as medical examiner, district attorney, lawyer, reporter, private investigator etc.

It would be great if most of the stories in the series dealt with serial killers—as opposed to cults, human trafficking, organized crimes etc—but it's not necessary.

The romance between the two protagonists should be developed over the series. Ideally there should be no love-triangle but if there is one then it should be resolved within the first ten to twelve books.

There can be some paranormal element but not too much of it.

The books should be written in third person.

The books should be set in the US.

Please add only the first book of the series.

Thank you :-)