Im Gerichtssaal gibt der Angeklagte alles zu.

Im is a contraction of in dem.

• in dem Gerichtssaal → im Gerichtssaal

Here, Gerichtssaal is masculine: der Gerichtssaal.
Because the sentence is talking about location, German uses the dative after in:

• der Gerichtssaal → dem Gerichtssaal

So:

• in dem Gerichtssaal = im Gerichtssaal = in the courtroom

The noun itself is masculine: der Gerichtssaal. Like grammatical gender in German generally, this is something you usually have to learn with the noun.

It helps to learn nouns with their article:

• der Gerichtssaal = the courtroom

That way, when you need other forms, they are easier to produce:

• nominative: der Gerichtssaal
• dative: dem Gerichtssaal
• contracted with in dem: im Gerichtssaal

German often puts a time, place, or other element first for emphasis or style. The verb still has to stay in the second position in a main clause.

So the structure is:

• Im Gerichtssaal = first element
• gibt = second-position verb
• der Angeklagte = subject

That is why you get:

• Im Gerichtssaal gibt der Angeklagte alles zu.

If you started with the subject instead, that would also be correct:

• Der Angeklagte gibt im Gerichtssaal alles zu.

Both are grammatical; the first version emphasizes the setting a bit more.

Because in German main clauses, the finite verb must be in position 2.

Since Im Gerichtssaal has been placed first, the verb comes next:

1. Im Gerichtssaal
2. gibt
3. der Angeklagte
4. alles
5. zu

This often feels unusual to English speakers, but it is very normal in German. The subject does not always come first.

Der Angeklagte means the defendant or the accused man.

It comes from the adjective/participle angeklagt and is being used like a noun. In this sentence it is masculine singular and is the subject, so it takes nominative:

• der Angeklagte = the defendant

If it were a woman, you would say:

• die Angeklagte

Because the verb is zugeben, which is a separable verb.

Its basic form is:

• zugeben = to admit, confess, acknowledge

In a normal main clause, the prefix separates and moves to the end:

• Ich gebe es zu. = I admit it.
• Der Angeklagte gibt alles zu.

So:

• gibt = the conjugated main part
• zu = the separable prefix

This is very common in German. A verb with a prefix can have a meaning that is not fully predictable from the base verb.

• geben = to give
• zugeben = to admit / confess

So you should learn zugeben as its own vocabulary item, not as a literal give to.

Alles zugeben means to admit everything or to confess to everything.

• alles = everything
• alles zugeben = to admit everything

In context, it usually means the defendant is admitting all the accusations or all the relevant facts.

Alles is the correct pronoun meaning everything.

Here it functions as the object of zugeben. German often uses alles very simply:

• Ich weiß alles. = I know everything.
• Er erzählt alles. = He tells everything.
• Sie gibt alles zu. = She admits everything.

There is no form like alleses here.

• der Angeklagte is nominative, because it is the subject.
• alles is accusative, because it is the direct object of zugeben.

So the sentence structure is:

• Im Gerichtssaal = prepositional phrase in the dative
• gibt = finite verb
• der Angeklagte = nominative subject
• alles = accusative object
• zu = separable prefix

Yes, that is grammatically possible.

German word order is flexible, as long as the main rules are respected:

• the finite verb is in second position
• the separable prefix stays at the end in a main clause

So these are both correct:

• Im Gerichtssaal gibt der Angeklagte alles zu.
• Der Angeklagte gibt im Gerichtssaal alles zu.

The first version foregrounds in the courtroom a little more.

In a subordinate clause, the verb is no longer split in the same way. The full infinitive-like form appears together at the end.

For example:

• ..., weil der Angeklagte alles zugibt. = ... because the defendant admits everything.

Notice that in the subordinate clause:

• zugibt is written as one word at the end

That is different from the main clause:

• Der Angeklagte gibt alles zu.

Usually it means admit or confess, depending on context.

• alles zugeben = to admit everything / confess everything

It does not automatically mean the formal legal act of pleading guilty. If the context is a courtroom, English might sometimes translate it that way loosely, but grammatically the German verb itself is simply zugeben.

So the idea is: the defendant is admitting everything, not necessarily using a technical legal formula.