Copy and Paste from another resource:
A suicide scene is treated as a crime scene. If the suicide took pace in the home and if people are present in that home when the body is discovered the police immediately separate all the people in the house and they are questioned as to what took place prior to discovering the body. There answers will not be exactly the same however, they should be a certain amount of consistency between the stories.
In the case of a child taking their life the parents are separated as are the siblings and they are asked multiple questions which are later discussed with other law enforcement officers.
The police will search for a note and all clothing of the victim is wrapped in clear plastic and is considered evidence and is forensically examined.
During the time the police are interrogating witnesses they are looking for specific reactions. People at the time of a trauma will go into shock. They pace and they and they are cold to the touch. They repeatedly ask to go to the hospital to be with the victim and they ask if their loved one is still alive.
The police will ask how the victim was behaving prior to the suicide and whether the victim has a history of mental illness.
Regardless of the hour or the day of the week the police will have notified the victim's school or place of employment and go through personal papers or school work look for signs of depression.
The interrogation of family, friends, school officials, employer and the physician is used to put to put together a psychological autopsy to look for a history of mental illness, bullying, or emotional and mental issues, isolation, depression, lack of friends or family support and suicide threats or suicide behavior such as attempts, threatening suicide prior to the suicide and a drastic and consistent change in what is considered normal behavior of the suicide weeks before the suicide occurred.
The police are trained what to look for and although no two suicides are the same there is consistencies. police take a quick look but do not touch the body. They are looking for bruises and wounds on the body to see if there was a struggle before the death.
The police know if something is not routine immediately as they have attended to hundreds if not thousands of suicides. The police also will call in detectives if they feel the death is suspicious.