Svjedok krađe zna tko je pokušao ukrasti bicikl.

Because krađe is the genitive singular of krađa (theft).

In svjedok krađe, Croatian uses the genitive after a noun to show a relationship like:

• svjedok nesreće = witness of the accident
• uzrok problema = cause of the problem
• početak filma = beginning of the film

So svjedok krađe literally means witness of the theft, or more naturally in English, a witness to the theft.

Croatian does not have articles like English a/an and the.

So:

• svjedok can mean a witness or the witness
• bicikl can mean a bicycle or the bicycle

The exact meaning depends on context. In a real conversation, people would understand from the situation whether the speaker means a specific witness or bicycle.

It is an embedded question (also called an indirect question).

The main clause is:

• Svjedok krađe zna = The witness knows

And what does the witness know?

• tko je pokušao ukrasti bicikl = who tried to steal the bicycle

So the whole structure is:

• X zna tko... = X knows who...

This is not a direct question. A direct question would be:

• Tko je pokušao ukrasti bicikl? = Who tried to steal the bicycle?

Here, that question is embedded inside a larger sentence.

Tko is the standard Croatian form for who.

You may also hear ko in speech, especially in more casual or regional usage, but:

• tko = standard / preferred in formal writing
• ko = colloquial in many varieties

So in a textbook-style sentence, tko is exactly what you would expect.

This is because Croatian past tense uses:

• the auxiliary je
• plus the past participle pokušao

So je pokušao = tried

Also, Croatian has a strong tendency for short unstressed words called clitics—like je—to appear near the beginning of the clause, often in second position.

So:

• tko je pokušao is the natural order

Here:

• tko = first element
• je = clitic in second position
• pokušao = main participle

That is why tko je pokušao sounds normal.

It is the perfect tense of pokušati (to try).

Croatian perfect tense is formed with:

• present tense of biti (to be)
• plus the l-participle

So here:

• je = has/is auxiliary, 3rd person singular
• pokušao = masculine singular past participle of pokušati

Together:

• je pokušao = tried / has tried

In normal English, we translate it here simply as tried.

Also notice that pokušao is masculine singular. With tko (who), Croatian normally uses masculine singular as the default form when the person is unspecified.

This is about aspect, which is very important in Croatian verbs.

• krasti = imperfective
• ukrasti = perfective

Very roughly:

• krasti focuses more on the process, repetition, or ongoing nature of stealing
• ukrasti focuses on the act as a whole, with a result/completion

After pokušati (to try), Croatian often uses a perfective infinitive when talking about a single specific action:

• pokušao ukrasti bicikl = tried to steal the bicycle

That sounds very natural here because this is one specific attempted theft.

If you said pokušao krasti, it would sound less natural in this context and would suggest a different nuance.

Bicikl is in the accusative singular, because it is the direct object of ukrasti.

You steal something, so that thing goes in the accusative:

• ukrasti bicikl = to steal a bicycle / the bicycle

The reason the form looks unchanged is that masculine inanimate nouns in Croatian often have:

• nominative singular = accusative singular

So:

• nominative: bicikl
• accusative: bicikl

Same form, different grammatical function.

Compare that with a masculine animate noun, where accusative usually changes:

• nominative: student
• accusative: studenta

Yes. In the main clause, svjedok krađe is the subject.

The structure is:

• Svjedok krađe = subject
• zna = verb
• tko je pokušao ukrasti bicikl = object/content clause

So the witness is the one who knows.

Inside the embedded clause, the subject is tko:

• tko je pokušao ukrasti bicikl = who tried to steal the bicycle

So the sentence has:

• a main clause subject: svjedok krađe
• an embedded clause subject: tko

Here zna clearly means knows in the sense of has the information.

Croatian znati can mean:

• to know a fact
• to know how to do something

Examples:

• Znam odgovor. = I know the answer.
• Znam plivati. = I know how to swim.

In this sentence:

• zna tko je pokušao ukrasti bicikl

it means the witness knows which person did it.

It does not mean being acquainted with someone in the sense of I know him/her personally. For that, Croatian often uses poznavati or context makes the meaning clear.

Croatian word order is fairly flexible, but this version is the most neutral and natural.

The given sentence:

• Svjedok krađe zna tko je pokušao ukrasti bicikl.

is straightforward and standard.

You might move things around for emphasis, but the original is the best default choice for learners.

For example, changing word order could emphasize a different part, but it may sound marked rather than neutral. So if you are learning, this is a good pattern to copy:

• [subject] + [verb] + [embedded question]

That pattern is very common in Croatian.