It could be as simple as a photo of a car, an outfit seen at the scene of a crime or a conversation between Facebook "friends."
Or, as seen this week in Cleveland, evidence found on social media could take a more extreme turn.
Nonetheless, as people regularly turn to the Internet to post the every-day happenings of their lives, police are also using popular sites like Facebook and Instagram to weed out clues that could help them incriminate suspects.
"Every police department uses social media to find information," said North Attleboro Police Captain Joseph DiRenzo.
Police don't necessarily comb through sites without a purpose - but when a suspect's name comes to light, DiRenzo said Facebook, Instagram, Twitter and other popular social media sites are useful tools police can use
to tie a suspect to a crime.
"The best way to use it is to connect people together," DiRenzo said. "Are these people still in touch? Are they still living in the area? Sometimes it leads us to friends we were looking for."
Other times, offenders themselves might unknowingly post content that could later incriminate them.
"We can look for certain clothing in pictures from certain days," DiRenzo said, which is useful when police have a description of a suspect in a particular crime. "Recently in an armed robbery case we knew what kind of car was used, and a suspect had posted pictures of the car or with the car on their social media page. Pictures of people with guns. It's been helpful in that way."
And, sometimes, evidence is posted online on purpose - perhaps for attention from peers or because the lawbreakers doubt police will catch onto their scheme.
Cleveland police stumbled across perhaps their biggest piece of online evidence last week when a Cleveland man posted a live Facebook video as he shot another man.
The suspect, Steve Stephens, allegedly walked up to a 74-year-old stranger on the street and fatally shot him as he streamed the shooting on social media.
Police were able to track Stephens to Erie, Pa., just a few days later with the help of a public tip. But as they approached his vehicle, Stephens allegedly led police on a car chase for about a mile before committing suicide behind the wheel.
Cases like that are rare, but in North Attleboro, DiRenzo said he has seen plenty of people incriminate themselves on social media.
The most popular way is when someone puts items up for sale online that police know have been stolen.
"It might not have been them, but they may know where it came from," DiRenzo said.
Teens are often known to post videos of fist fights online - and while, it's not something police are actively searching for, the online evidence can come in handy if the department receives a complaint, DiRenzo said.
Sometimes the social media clues are even brought directly to them.
"Once it's out there, it's out there," DiRenzo said.
In any case, the posts are a stepping stone for police to start from.
That is, if they're readily accessible.
Police don't receive special access to the websites, so many times they are limited to the same content the public sees.
But, many people leave their Facebook and Instagram pages open to the public.
As Attleboro police Chief Kyle Heagney put it: "What the oil man or the milk man can see, the policeman can see."
"It's open source information," Heagney said. "It's all public information so there's not a Fourth Amendment issue there."
The Fourth Amendment protects an individual's right to against unreasonable searches and seizures of private property without a warrant.
But when social media sites are open to the public, they're free game for police too.
Attleboro Lt. Timothy Cook said his staff looks for pictures and conversations that might place someone in the area of a crime under investigation or associate them with other known members of a crime.
"It's an investigative tool," he said.
But, social media is useful in clearing someone from a crime as well, he said.
"It's just as important to identify a falsely accused party, just as it is a guilty party."