Photos of firearms, corpses and a Valencia High School sign led police to believe a Los Angeles area high school student was planning a school massacre, but it was really just a prank? The 15-year-old high school student was arrested on Sunday after making threats of a mass shooting on Instagram.

Police originally began investigating the matter on Saturday, after they had received more than 24 calls about Instagram posts from a teen threatening to shoot students at a local high school, according to a report in the Associated Press.

"Valencia High School has been nominated to be shot up first," read one of the posts, according to the report.

The unnamed teen had his home searched and no weapons were found. Police said the teen just wanted to get a reaction from his friends, but had no intention of carrying out any of the murderous actions hinted at in his social media posts.

Also in Southern California, police investigators may have stopped a high school massacre, according to reports, after they arrested two teens who they say planned to kill staffers and students in South Pasadena, CA.

Two unnamed boys, one 16 and the other 17, were closely monitored online after school officials allegedly found out about a plot the teens were working on.

Both of the teens would have been entering their senior year in high school, but were arrested for making "threats and conspiracy," according to police.

The two were put into juvenile detention facilities. The FBI was working with local police to dig into the teen's computers, which had information about the plans the two minors were allegedly compiling for their attack.

Detectives told the Associated Press that they had done nearly a week of surveillance on the Internet and followed the boys' searches and claimed that, "They had a plan in mind that they were going to execute."

The duo was allegedly searching for information on guns, knives, bombs and tactical techniques, the report said.

The two boys had three high school staffers that they had planned on killing, police said, citing messages that were going back and forth between the two youths.

They had also talked about massacring as many students as they could, South Pasadena Police Chief Arthur Miller told the press. The plot is being described as "cold-hearted," according to one report. 

Police officials couldn't provide specifics on the case, nor could they name the teens because they are minors. Students at the school were shaken up by the news, and some told the media they were worried about the first day of school, which starts on Thursday.

School officials did not reveal how they found out about the plot, but police officials acted quickly, saying that lives were saved by the quick response and arrest of the students.

"They were making a huge, huge plan of a school massacre," the police chief Miller said, stating that they teens were very real about their intentions to "kill as many people as possible."

Police were able to obtain warrants to arrest the boys and said they broke into his home, and he tried to run away. The other boy was trying to get a weapon from one of his relatives, but wasn't able to.