In the scene where he and Simmons are at gunpoint and Simmons forces him to drop his gun, you can clearly see him tear up and a tear fall from his eye. Very odd, to say the least.
I'm happiest...in the saddle.
Most likely it was from tear gas, but also Ramsey had a fear of heights and it caused him to let a killer escape from him and a family was killed. In the scene you are referring to, Ramsey is being forced to drop his gun which might mean Luther escapes and then kill more people. Ramsey is remembering the former case and he tears up.
Watch the movie again and you will hear reference to the former case.
"Watch the movie again and you will hear reference to the former case."
Do I have to?