terrified of my 5 year old

Someone please help me.. I don’t think I am overreacting. I have an older son who will be 5 in July, a 15 month old son, and a daughter due in 2 weeks. Recently, my older son has been saying really weird scary things when he’s always been a pretty caring, loving boy even when he’s super crazy and hyper. A few weeks ago, he started saying things about the devil. He was hitting himself in the head (which he’s never done) and I asked why he was doing that and he said “the devil is in my head.” I freaked out! I said “okay, and what does the devil say?” and he replied with “to kill” and just laughed about it. It literally freaked me out. I don’t really talk about the devil with him besides explained Heaven and Hell a few times and who God and the Devil are(we are catholic). Sometimes we pray and I would read some kids Bible books to him. Ever since he said the devil was in his head, we say a nightly prayer. Tonight is what really scared me though... he just got off the phone with his dad and then I called to FaceTime my mom. I was talking to her and didn’t catch what my son said but her and my husband did. He said “kill the baby, kill the people” and they told me he had just said that and asked what he said to repeat it to make sure they caught it right. He refused to answer them. After we got off the phone, I sat down with him and asked him to repeat what he said and sure enough, they heard correctly. I asked who is “the baby” and he said Giovanni.. his younger brother(I asked because I wasn’t sure if he was talking about his sister fue in 2 weeks). I was like okay... why would you say those things and all he had to say was “I dunno.” This is definitely not normal behavior for him or I think ANY child. What do I do? Take him to a therapist... i don’t know. I’m at a loss.

Edit to add:

He does not attend any childcare/daycare and he won’t start school until later this year. He doesn’t have unsupervised internet access. He has a children’s kindle, but I control all the apps and games and books that are on it from my Amazon so he can’t download anything without me approving or seeing it first and it doesn’t have access to YouTube/any videos without me seeing them.