A soldier who killed three colleagues and injured 16 others in a shooting at US Army base was being treated for depression and anxiety.
He was also being assessed for post-traumatic stress disorder (PTSD).
What is PTSD?
Post-traumatic stress disorder is an anxiety disorder caused by witnessing or being involved in a frightening or distressing event.
People naturally feel afraid when in danger, but the legacy of some traumatic events is a change in perception of fear.
They may feel stressed or frightened in day-to-day life.
What can trigger it?
Any traumatic event has the potential to lead to PTSD including:
- military conflicts
- serious road accidents
- natural disasters
- sexual assaults
People will be generally affected within one month of the event.
How is it diagnosed?
There is no blood test for PTSD, it instead relies on the judgement of a doctor speaking to their patient about their symptoms.
There must have been an initial traumatic event involving a close brush with death or serious violence.
There are then four criteria which must be present:
- re-experiencing the event - commonly known as flashbacks
- avoidance behaviour - people will not talk about the event and avoid anything that reminds them of it
- sleep impact - they will have poor sleep quality and be irritable
- mood change - commonly a perception that something bad is always about to happen
"This has to impair day-to-day function," said Neil Greenberg, a defence professor of mental health at the King's College London.
Is it easy to diagnose?
"With properly skilled doctors it can be very easy to diagnose, it could take a few hours," says Prof Greenberg.
But he says doctors must have a good suspicion of PTSD before starting to diagnose someone, as patients may not bring up their trauma history.
It can also be a challenge because some people deliberately "overinflate symptoms", sometimes for financial reasons, while others seek to avoid the stigma of a PTSD diagnosis.
How is it treated?
For many people, the symptoms will go away within a month - but others will need psychotherapy or, if that fails, medication.
Cognitive behavioural therapy can help change the way people think about the traumatic event in order to control fear and anxiety.
This involves going through the event in detail with a therapist.
Antidepressants, such as paroxetine, are used if psychotherapy does not work.
Prof Greenberg, who also works with the UK Psychological Trauma Society, says treatment is still effective many years after the incident.
However, after such a long time the symptoms are very unlikely to clear up without treatment.