Learn Swedish: Jag sitter och hoppas mördaren sviker dem. - I sit and hope the killer betrays them.

Just like in English, you can often leave out the word for "that" (att) when it links to a new clause. You could absolutely say Jag sitter och hoppas att mördaren sviker dem, but dropping att is very common and makes the sentence flow more naturally in spoken Swedish.

Why say sitter och hoppas instead of just jag hoppas?

Swedish doesn't have an "-ing" form to show an ongoing action (like "I am hoping"). Instead, it often pairs a verb of position (like sit, stand, or lie) with och (and) plus the main verb. Jag sitter och hoppas is the natural Swedish way to express "I am sitting here hoping."

Why does hoppas end in an "-s"? Is it a passive verb?

No, it is active! Hoppas is a "deponent" verb. These are special verbs that always end in -s but have a normal, active meaning. Other common examples include andas (breathe), minnas (remember), and trivas (enjoy oneself).

How does mördare (killer) become mördaren (the killer) without adding "-en"?

The base noun is en mördare. When an en-word already ends in a vowel, especially the -are ending for people who do an action, you only add an -n to make it definite (the killer), rather than adding another syllable.