Identify the following quoted word as a gerund, participle, or infinitive. the thief confessed to 'stealing' the camera from the display. type of verbal:

The word 'stealing' is a gerund. 

A gerund is basically a verb that functions as a noun. A gerund can be identified as follows: a verb+ 'ing'.

Here, 'stealing' is a gerund because it has the pattern: verb (steal) + 'ing' = stealing

Other examples of gerunds include; 'running', 'playing', 'sweating' and 'projecting'.

The combined sentence uses a compound subject.

Explanation

The subject of a sentence is said to be the protagonist.  

It maybe a person, place, or idea.  compound subject using sentences has multiple subjects (two or more) joined by 'and' or 'or'.

When using multiple subjects, the use of subject-verb agreement is important to express the proper idea of the sentence.

Here,  Sir Edmund and Cecil are subjects.

As there are two subjects, this is a sentence that uses two subjects, hence it is a compound subject.