ものと思われる / ものと見られる【ものとおもわれる / ものとみられる】

ものと思われる and ものと見られる mean "it is believed that", "is thought to": the writer presents a conclusion without claiming it as fact or as their own opinion. They go after the plain form, present or past; a な-adjective takes な and a noun takes である.

Both are passive, so nobody is named as the one who thinks. That is what makes them the voice of news reports, police statements and academic papers.

思われる or 見られる

The two are often interchangeable. ものと思われる leans towards reasoning – this is what the facts suggest. ものと見られる leans towards an outside assessment – this is how investigators or analysts see it – and is the more frequent of the two in news.

With ている, みられている見られている and おもわれている思われている report a view that is already widely held.

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These are written forms, or the spoken forms of a newsreader. In conversation, giving your own view, say とおもう思う or みたいだ. Used in a chat, ものと思われる sounds like a press release.