Legal term for a person suspected of a crime, used in criminal procedure contexts. More formal than 容疑者, which is common in news reports.
See also: 容疑者
The police took the suspect into custody.
The suspect has the right to remain silent.
The police arrested the man as a suspect.
The detective is interrogating the suspect.
The prosecutor's office took the suspect into custody.
The suspect confessed to the incident.
被疑者 is the person suspected of committing a crime, while 被害者 is the person who suffered from it.
Compound of 被 (ひ, 'receive, incur') + 疑 (ぎ, 'doubt, suspicion') + 者 (しゃ, 'person'). The exact historical derivation is uncertain, but the kanji combination transparently means 'person under suspicion'.